Light emitting diode

ABSTRACT

The invention provides a light emitting diode. The light emitting diode includes a ceramic substrate having a first surface and an opposite second surface. A first conductive trace metal layer and a second conductive trace metal layer are disposed on the first surface of the ceramic substrate. At least one light emitting diode chip is disposed on the first surface of the ceramic substrate, respectively and electrically connected to the first and second conductive trace metal layers. A plurality of thermal metal pads is disposed on the second surface of the ceramic substrate, wherein the thermal metal pads are electrically isolated from the light emitting diode chip.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Taiwan Application No. 98126500,filed on Aug. 6, 2009, the entirety of which is incorporated byreference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting diode, and inparticular, to a light emitting diode having a plurality of thermalmetal pads.

2. Description of the Related Art

Light emitting diodes (LEDs) are solid-state light sources havingadvantages of having low power consumption, a small size, fast operatingspeeds, long lifespans, less attenuation, solid appearance, good shockresistance, and a simple fabrication process, thereby promoting LED useinstead of traditional light sources. However, for LEDs applied asbacklights and electrical illuminations, a heat dissipation problemstill exists. To solve the heat dissipation problem, a thermal metal paddisposed on a ceramic substrate of the conventional LEDs is design as asingle structure with a large area. When the conventional single thermalmetal pad bonds to a circuit substrate below the conventional LEDs bysoldering, however, the uneven surface of the ceramic substrate resultsin non uniform cohesion of the solders, thereby forming gas hole residueand cracks at an interface between the conventional single thermal metalpad and the circuit substrate. Therefore, the interface between theconventional single thermal metal pad and the circuit substrate has poorbonding. Also, when the conventional LEDs are operated, generated heatstress results in a continuous glowing crack along gas holes due to thelarge area of the conventional single thermal metal pad. Therefore, LEDsmay detach from the circuit substrate at the interface therebetween,thereby reducing electrical performance, heat dissipation area, heatdissipating efficiency and reliability.

Thus, a novel light emitting diode with high heat dissipating efficiencyand reliability is desired.

BRIEF SUMMARY OF INVENTION

A light emitting diode is provided. An exemplary embodiment of a lightemitting diode has a plurality of the thermal metal pads with smallareas. Each solder can firmly adhere to corresponding thermal metalpads. Therefore, reducing a gas hole generation problem. If a crackoccurs in one of the thermal metal pads due to a poor bonding interface,the generated crack is limited to the same thermal metal pad and doesnot affect adjacent thermal metal pads. If one of the thermal metal padsdetaches from the circuit substrate at an interface therebetween, thebonding between adjacent thermal metal pads and the circuit substratewill not be affected. Therefore, electrical performance and reliabilityof the light emitting diode is maintained, thereby maintaining heatdissipating efficiency thereof.

An exemplary embodiment of a light emitting diode comprises: a ceramicsubstrate having a first surface and an opposite second surface; a firstconductive trace metal layer and a second conductive trace metal layerdisposed on the first surface of the ceramic substrate; at least onelight emitting diode chip disposed on the first surface of the ceramicsubstrate, respectively and electrically connected to the first andsecond conductive trace metal layers; and a plurality of thermal metalpads disposed on the second surface of the ceramic substrate, whereinthe thermal metal pads are electrically isolated from the light emittingdiode chip.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 a is a top view showing one exemplary embodiment of a lightemitting diode of the invention.

FIGS. 1 b and 1 c are top views of other exemplary embodiments of alight emitting diode of the invention showing various electricalconnections of the light emitting chip.

FIG. 1 d is a bottom view showing one exemplary embodiment of a lightemitting diode of the invention.

FIG. 1 e is cross section view taken along line A-A′ of FIG. 1 a showingone exemplary embodiment of a light emitting device connected to acircuit substrate.

DETAILED DESCRIPTION OF INVENTION

The following description is of a mode for carrying out the invention.This description is made for the purpose of illustrating the generalprinciples of the invention and should not be taken in a limiting sense.The scope of the invention is best determined by reference to theappended claims. Wherever possible, the same reference numbers are usedin the drawings and the descriptions to refer the same or like parts.

The present invention will be described with respect to particularembodiments and with reference to certain drawings, but the invention isnot limited thereto and is only limited by the claims. The drawingsdescribed are only schematic and are non-limiting. In the drawings, thesize of some of the elements may be exaggerated and not drawn to scalefor illustrative purposes. The dimensions and the relative dimensions donot correspond to actual dimensions to practice the invention.

FIG. 1 a is a top view showing one exemplary embodiment of a lightemitting diode 500 of the invention. To describe disposition of lightemitting diode chips 206 and the conductive trace structure, a packagingadhesive 212 of the light emitting diode 500 as shown in FIG. 1 e is notillustrated herein for brevity. FIGS. 1 b and 1 c are top views ofexemplary embodiments of light emitting diodes 500 a and 500 b of theinvention showing various electrical connections of light emitting chips206 a. FIG. 1 d is a bottom view showing one exemplary embodiment of alight emitting diode 500 of the invention. FIG. 1 d also illustrates abottom view showing one exemplary embodiment of a light emitting diode500 a or 500 b. FIG. 1 e is cross section view taken along line A-A′ ofFIG. 1 a showing one exemplary embodiment of a light emitting device 500connected to a circuit substrate 222. As shown in FIGS. 1 a to 1 d, oneexemplary embodiment of a light emitting device 500 may comprise aceramic substrate 200, a plurality of light emitting diode chips 206, aconductive trace structure and a plurality of thermal metal pads 216. Inone embodiment, the ceramic substrate 200 has a first surface 202 and asecond surface 204 opposite to the first surface 202. In one embodiment,the ceramic substrate 200 may comprise aluminum nitride (AlN) oraluminum oxide (Al₂O₃). A plurality of light emitting diode chips 206 isdisposed on the first surface 202 of the ceramic substrate 200. In oneembodiment as shown in FIG. 1 a, the light emitting diode chip 206 has ap-type electrode and an n-type electrode (not shown) respectively on atop surface and a bottom surface of the light emitting diode chip 206.Note that the disposition of the p-type and n-type electrodes may beswitched according to design of the light emitting diode chip 206. Asshown in FIGS. 1 a, 1 d and 1 e, the conductive trace structure maycomprise a first conductive trace metal layer 208 a and a secondconductive trace metal layer 208 b directly disposed on the firstsurface 202 of the ceramic substrate 200, a third conductive trace metallayer 208 c disposed between the ceramic substrate 200 and the lightemitting diode chips 206 electrically connecting to the light emittingdiode chips 206, conductive traces 209 electrically connected betweenthe light emitting diode chips 206 and the second conductive trace metallayer 208 b or third conductive trace metal layer 208 c, and fourth andfifth conductive trace metal layers 208 d and 208 e disposed on thesecond surface 204 of the ceramic substrate 200. In one embodiment, theconductive trace structure may be used as an electrical connection pathfor input/output (I/O) signals, ground signals, and power signals of thelight emitting diode chips 206. Additionally, as shown in FIG. 1 d, inone embodiment, the first conductive trace metal layer 208 a of theconductive trace structure may be electrically connected to the fourthconductive trace metal layer 208 d disposed on the second surface 204 ofthe ceramic substrate 200 by a via 214 a formed through the ceramicsubstrate 200. Similarly, the second conductive trace metal layer 208 bof the conductive trace structure may be electrically connected to thefifth conductive trace metal layer 208 e disposed on the second surface204 of the ceramic substrate 200 by a via 214 b formed through theceramic substrate 200. Therefore, as shown in FIG. 1 e, the conductivetrace structure may extend on the second surface 204 of the ceramicsubstrate 200, thereby being electrically connected to the circuitsubstrate 222, which connects to the second surface 204 of the ceramicsubstrate 200. In one embodiment, the conductive trace structure maycomprise Ag, Cu, Ni, Al or combinations thereof. As shown in FIG. 1 e,one exemplary embodiment of the light emitting device 500 furthercomprises a packaging adhesive 212 encapsulating the first surface 202of the ceramic substrate 200, the light emitting diode chips 206, thefirst conductive trace metal layer 208 a, the second conductive tracemetal layer 208 b, the third conductive trace metal layer 208 c and theconductive traces 209. The packaging adhesive 212 may prevent the lightemitting diode chips 206 from damage. Also, the packaging adhesive 212may allow output of light emitted from the light emitting diode chips206. In one embodiment, the packaging adhesive 212 may comprise materialsuch as silicon, epoxy, fluorescent glue or combinations thereof.

FIGS. 1 b and 1 c are top views of other exemplary embodiments of lightemitting diodes 500 a and 500 b of the invention showing variouselectrical connections of the light emitting chips 206 a. As shown inFIG. 1 b, the light emitting diode chip 206 a has a p-type electrode andan n-type electrode (not shown) both on the top surface of the lightemitting diode chip 206 a. The p-type electrode and the n-type electrodeare respectively and electrically connected to the first conductivetrace metal layer 208 a and the second conductive trace metal layer 208b through the conductive traces 209. Therefore, the light emitting diodechips 206 a are connected in series. It is noted that in alternativeembodiments as shown in FIG. 1 c, the light emitting diode chips 206 aare respectively and electrically connected to the first conductivetrace metal layer 208 a and the second conductive trace metal layer 208b through the conductive traces 209. Therefore, the light emitting diodechips 206 a are connected in parallel. As shown in FIGS. 1 b, 1 c, 1 dand 1 e, the conductive trace structure of the light emitting diodes 500a and 500 b may comprise a first conductive trace metal layer 208 a anda second conductive trace metal layer 208 b directly disposed on thefirst surface 202 of the ceramic substrate 200, a third conductive tracemetal layer 208 c disposed between the ceramic substrate 200 and thelight emitting diode chips 206, electrically connecting to the lightemitting diode chips 206 a, conductive traces 209 electrically connectedbetween the light emitting diode chips 206 a and the second conductivetrace metal layer 208 b or third conductive trace metal layer 208 c, andfourth and fifth conductive trace metal layers 208 d and 208 e disposedon the second surface 204 of the ceramic substrate 200.

As shown in FIGS. 1 d and 1 e, one exemplary embodiment of a lightemitting diode 500 further comprises a plurality of thermal metal pads216 disposed on the second surface 204 of the ceramic substrate 200. Thethermal metal pads 216 may dissipate heat generated from the lightemitting diode chips 206 to the outside atmosphere. In one embodiment,surfaces of the thermal metal pads 216 away from the ceramic substrate200 and surfaces of the fourth and fifth conductive trace metal layers208 d and 208 e are coplanar, thereby ensuring the fourth and fifthconductive trace metal layers 208 d and 208 e and the thermal metal pads216 to have good electrical connections with the circuit substrate 222connected to the second surface 204 of the ceramic substrate 200. Aplurality of the thermal metal pads 216 are electrically isolated fromeach other at a distance d. Additionally, the thermal metal pads 216 areelectrically isolated from the light emitting diode chips 206, thefourth and fifth conductive trace metal layers 208 d and 208 e.

As shown in FIG. 1 e, in one exemplary embodiment of a light emittingdiode 500, the fourth and fifth conductive trace metal layers 208 d and208 e disposed on the second surface 204 of the ceramic substrate 200and the thermal metal pads 216 are bonded to the circuit substrate 222through solders by soldering. For example, the fourth conductive tracemetal layer 208 d may connect to the bonding pad 224 a of the circuitsubstrate 222 by a solder 228 a. The fifth conductive trace metal layer208 e may connect to the bonding pad 224 b of the circuit substrate 222by a solder 228 b. The bonding pads 224 a and 224 b are used to transmitinput/output (I/O) signals, ground signals, and power signals of thelight emitting diode chips 206. Additionally, the thermal metal pads 216may connect to a plurality of bonding pads 226 of the circuit substrate222 by solders 228 c. Therefore, the bonding pads 226 may dissipate heatgenerated from the light emitting diode chips 206 to the outsideatmosphere through the circuit substrate 222. In one embodiment, thebonding pads 226 connecting to the thermal metal pads 216 may have thesame size and number with the thermal metal pads 216. Alternatively, thethermal metal pads 216 may also be bonded to a single bonding pad havinga larger area (not shown).

One embodiment of the light emitting diode 500 having a plurality of thethermal metal pads 216 isolated from each other has the advantages asfollows. The thermal metal pads 216 disposed on the ceramic substrate200 are numerous, having smaller bonding areas. Despite unevenness ofthe ceramic substrate 200, each solder can firmly adhere tocorresponding thermal metal pads 216. Therefore, reducing the gas holegeneration problem. If a gas hole is generated at an interface betweenone of the thermal metal pads 216 and the circuit substrate 222 due topoor bonding, gas is immediately exhausted to the outside atmosphere.Therefore, reliability of the light emitting diode is not seriouslyaffected. Also, if a crack occurs in one of the thermal metal pads 216due to poor bonding, the generated crack would be prevented fromworsening, due to the spacing d between the thermal metal pads 216.Therefore, the generated crack would be limited to the thermal metal pad216 without affecting adjacent thermal metal pads. The spacing betweenthe thermal metal pads 216 may serve to limit probability of detachmentdue to poor bonding of one thermal metal pad 216. For example, if one ofthe thermal metal pads 216 detaches from the circuit substrate 222 at aninterface between the thermal metal pads 216 and the circuit substrate222, bonding of adjacent thermal metal pads 216 and the circuitsubstrate 222 would not be seriously affected. Therefore, electricalperformance, reliability and heat dissipating efficiency of the lightemitting diode 500 are maintained, despite the detachment due to poorbonding of one thermal metal pad.

While the invention has been described by way of example and in terms ofthe preferred embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. To the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

1. A light emitting diode, comprising: a ceramic substrate having afirst surface and an opposite second surface; a first conductive tracemetal layer and a second conductive trace metal layer disposed on thefirst surface of the ceramic substrate, respectively; at least one lightemitting diode chip disposed on the first surface of the ceramicsubstrate, respectively and electrically connected to the first andsecond conductive trace metal layers; and a plurality of thermal metalpads disposed on the second surface of the ceramic substrate, whereinthe thermal metal pads are electrically isolated from the light emittingdiode chip.
 2. The light emitting diode as claimed in claim 1, furthercomprising a third conductive trace metal layer disposed on the firstsurface of the ceramic substrate, the light emitting diode chip disposedon the third conductive trace metal layer, electrically connected to thefirst conductive trace metal layer through the third conductive tracemetal layer, and the light emitting diode chip, electrically connectedto the second conductive trace metal layer.
 3. The light emitting diodeas claimed in claim 1, further comprising a conductive traceelectrically connected to the light emitting diode chip and the secondconductive trace metal layer.
 4. The light emitting diode as claimed inclaim 2, further comprising a conductive trace electrically connected tothe light emitting diode chip and the second conductive trace metallayer.
 5. The light emitting diode as claimed in claim 2, furthercomprising a conductive trace electrically connected to the thirdconductive trace metal layer and the first conductive trace metal layer.6. The light emitting diode as claimed in claim 1, wherein surfaces ofthe thermal metal pads away from the ceramic substrate are coplanar. 7.The light emitting diode as claimed in claim 1, wherein the thermalmetal pads are electrically isolated from each other.
 8. The lightemitting diode as claimed in claim 1, further comprising a fourthconductive trace metal layer and a fifth conductive trace metal layerdisposed on the second surface of the ceramic substrate, wherein thefirst and second conductive trace metal layers are respectively andelectrically connected to the fourth and fifth conductive trace metallayers through vias in the ceramic substrate.
 9. The light emittingdiode as claimed in claim 1, further comprising a packaging adhesiveencapsulating the first surface of the ceramic substrate and the lightemitting diode chip.
 10. The light emitting diode as claimed in claim 1,wherein the ceramic substrate comprises aluminum nitride (AlN) oraluminum oxide (Al₂O₃).
 11. The light emitting diode as claimed in claim1, wherein the thermal metal pads comprises Ag, Cu, Ni, Al orcombinations thereof.
 12. The light emitting diode as claimed in claim1, wherein the conductive trace metal layer comprises Ag, Cu, Ni, Al orcombinations thereof.
 13. The light emitting diode as claimed in claim1, wherein the packaging adhesive comprises silicon, epoxy, fluorescentglue or combinations thereof.
 14. The light emitting diode as claimed inclaim 1, wherein the thermal metal pads are respectively andelectrically connected to a plurality of bonding pads disposed on acircuit substrate.
 15. The light emitting diode as claimed in claim 1,wherein the thermal metal pads are respectively and electricallyconnected to a single bonding pad disposed on a circuit substrate.